Engine routes in Application Controller

Question

I have a before_filter hook in my main app's application controller that does something like: (It doesn't just put a link in the flash, there is a message, but it isn't relevant to the question, it just accesses the route in the method)

class ApplicationController < ActionController::Base
  before_filter :set_link

  def set_link
    flash[:notice] = items_path
  end
end

This works fine for the app, however when I go into the controllers for an engine I made I get the exception

No route matches {:controller=>"items", :action=>"index"}

I understand that when in the engine, the routes helpers are for the engine unless prefixed with main_app

So changing the method in the application controller to

  def set_link
    flash[:notice] = main_app.items_path
  end

Gets rid of the exception but I really don't want to have to do that. Is there another solution to getting the engine to recognize the main_app routes?

EDIT:

This also happens if the application layout calls path helpers. So if the engine is designed to integrated into the main_app's layout then this issue will crop there up too.

Answer 1

You can keep the isolate_namespace, as strongly recommended by Rails Engine guide, and do this:

# inside your main_app's config/routes.rb
Rails.application.routes.draw do
  root to: 'home#index'

  mount MyEngine::Engine, at: "/" 
end

# inside your engine's controller
module MyEngine
  class SomeController << ::ApplicationController
    # include main_app's route helpers
    helper Rails.application.routes.url_helpers

  end
end

And inside your gem, make sure all the url helpers are prefixed with the correct routing proxy method (e.g. my_engine.pages_path).

Your main_app's layout and engine's controller will route and link to those url helpers correctly to the main app. You don't have to add "main_app" prefix anywhere to the main app. The only downside is you're mounting your engine's routes at main_app's root path, which could collide with any routes by the same name. This is expected anyway if you were to do non-isolate_namespace.